supercapacitor

1. Supercapacitor materials
(more than a capacitor and different than a battery)
Presented by
Mahfooz Alam
Materials Engineering (M Tech)
17ETMM10
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2. What is a supercapacitor (SC)?
• Supercapacitors (SC’s) are energy storages having
similarities with both batteries and conventional
capacitors.
• Unlike batteries, SC’s store electrical energy, not
chemical energy. Unlike capacitors SC’s contain
moving ions.
• Supercapacitors have many names: electrochemical
capacitor (EC Capacitor), Electric double-layer
capacitor (EDLC), ultracapacitor, ... All meaning the
same thing. 2

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Supercapacitor
• Supercapacitors are energy storage devices with very high
capacity and a low internal resistance, that are able to store and
deliver energy at relatively higher rates as compared to batteries
• Energy storage which involves a simple charge separation at the
interface between the electrode and the electrolyte
• A supercapacitor consists of two electrodes, an electrolyte, and
a separator which isolates the two electrodes electrically.

4. Why supercapacitors……?
• Power is the amount of energy used or produced in a certain
amount of time.
• High Energy density (they store more energy per unit mass)
• High Power density (they can release energy more quickly).
• They can do large work in less time
(eg: In power start and in acceleration of vehicles, upcoming
technology of trams etc…)
• Supercapacitors have,
 Power densities greater than those of batteries and
 Energy density greater than those of conventional capacitors.
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5. Conventional capacitor
• Electrons are moved from one electrode and deposited
on the other, and charge is separated by a solid dielectric
between the electrodes.
• Have smooth current collector surfaces.
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Difference between a conventional capacitor, battery
and supercapacitor

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Battery
• Electron transfer occurs across the two electrodes with
the electrolyte as the medium
• The charge storage is by redox reaction
Difference between a conventional capacitor, battery
and supercapacitor

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Difference between a conventional capacitor, battery
and supercapacitor
Supercapacitor
• The two electrodes are separated by a liquid electrolyte
rich in ions which isolates the two electrodes electrically.
• It has rough electrode surfaces
• Redox reaction across the double layers

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History
 In 1957 a group of General Electric Engineers using porous carbon
electrode first noticed electric double layer capacitor effect.
• energy was stored in the carbon pores and it showed an
exceptionally high capacitance
 Later in 1966, a group of researchers at Standard Oil of Ohio
accidently rediscovered cell design which is made up of two layers of
activated charcoal separated by a thin porous insulator.
 In 1978 NEC finally introduce the term Supercapacitor and its
application was used to provide backup power for maintaining
computer memory
 Later researchers delved into supercapacitor which led to trying of
other composite as electrode material such as Metal Oxides and
Conducting Polymer etc.

9. Important characteristics of a supercapacitor:
• Use electrodes having high specific surface area and thinner
dielectrics
• Supercapacitor can be fully charged and discharged in seconds
• SC’s can be charged and discharged (cycles) even up to a million
times.
• SC’s have very low energy densities vs. batteries; - SC’s have very
high self-discharge vs. batteries.
• 100 times shorter than the conventional electrochemical cell
• Functions over a larger range of temperature
• The supercapacitor electrolyte usually has a breakdown voltage
of 3V, so it is allowed only to charge up to 2.75V (Even at this low
voltage, a supercapacitor can store nearly 100-times more energy
per unit weight than dielectric capacitors).
• The performance relies on factors such as electrochemical
properties of electrode materials used, electrolyte and voltage
range 9

10. How supercapacitor works
• In discharged state all the ions are distributed randomly within the
cell.
• When a voltage is applied to a supercapacitor, these solvated ions
form a double-layer of ions at each electrode
• In charged state all the positive ions travel to the negative terminal
and vice versa.
• Supercapacitors use high surface area electrode material with a
liquid electrolyte added to wet-out more surface area on each side
of the 2-electrode cell for greater charge storage.
• The electrolyte is a non-conductive liquid that has lots of ions
(atoms/molecules with a net charge).
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• Due to the high surface area a huge capacitance is
achieved but also a very low breakdown voltage rating
(due to the thinness of the double layer)
• Supercapacitors with capacitances in the hundreds to
thousands of Farads, but with voltage ratings of only a
few volts.
• In high-voltage applications, supercapacitors have to
be stacked in series to obtain the desired voltage
ratings.

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Electrochemical double layer capacitors (EDLCs)
• EDLCs, that store charge electro-statically
• No chemical reaction, which eliminates swelling observed in active
material which batteries demonstrate during charging and
discharging.
• Performance of EDLC can be adjusted depending on the type of
electrolyte used
Pseudocapacitors
• Pseudocapacitors store charge via faradic process which involves
the transfer of charge between electrode and electrolyte
• When a potential is applied reduction and oxidation takes place on
the electrode material, which involves the passage of charge across
the double layer, resulting in faradic current passing through the
supercapacitor cell.
Eg: metal oxides, conducting polymers.

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Hybrid
• hybrid system it offers a combination of both(EDLCs , pseudo
capacitance ) that is by combining the energy source of battery-like
electrode, with a power source of capacitor-like electrode in the
same cell
• With a correct electrode combination it is possible to increase the
cell voltage, which in turn leads to an improvement in energy and
power densities.
• Generally, the faradic electrode results in an increase of energy
density at the cost of cyclic stability, which is the main drawback of
hybrid devices compared to EDLCs
• three different types of hybrid supercapacitors, which can be
distinguished by their electrode configurations:
1. Composite,
2. Asymmetric and
3. Battery-type.

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ELECTRODE MATERIALS
 Among the parameters that rely on the type of electrode
materials used in supercapacitors are capacitance and charge
storage.
Some electrode materials are
1. Carbon materials
2. Metal oxide
3. Conducting polymers
4. Nano composites based electrode materials

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Carbon materials
Various forms of Carbon are the most used electrode materials in the
fabrication of supercapacitors.
Reasons are due to its
i) high surface area
ii) low cost
iii) availability
iv) established electrode production technologies

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• The storage mechanism used by carbon materials is electrochemical
double layer formed at the interface between the electrode and
electrolyte
• Having a high specific surface area in the case of carbon materials,
results in a high capability for charge accumulation at the interface
of electrode and electrolyte.
• When improving specific capacitance for carbon materials, apart
from pore size and high specific surface area, surface
functionalization must be considered.
• Examples of carbon materials used as electrode materials are
activated carbon, carbon aerogels, carbon nanotubes, graphene etc.

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Activated carbon (AC)
 large surface area, good electrical properties and moderate cost
 physical or chemical activation carbonaceous materials (e.g.
wood, coal nutshell etc.).
 surface areas are well developed up to 3000 m2/g.
 pore size distribution that consists of micropores (<2 nm),
mesopores (2–50 nm) and macropores (>50 nm)
Carbon matrix

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• Having a high specific surface area (SSA) of around 3000 m2/g, a
relatively small capacitance was obtained.
• This shows not all pores are effective during charge accumulation.
• Hence, even though the SSA in EDLC is an important parameter
when it comes to performance, some other aspects are also
considered in carbon materials that influence electrochemical
performance to great extent like pore size distribution
• Additionally, excessive activation results in large pore volume,
which in turn leads to drawbacks like low conductivity and
material density, which will lead to a low energy density and loss
of power capability
• It was observed that the capacitance of AC is higher in aqueous
electrolytes (ranging from 100 F/g to 300 F/g) as compared to
organic electrolytes (<150 F/g

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Graphene
• high electrical conductivity, chemical stability, and large surface
area
• it doesn’t depend on the distribution of pores at solid state
• Higher specific surface area (SSA) around 2630 m2/g.
• If the entire SSA is fully utilized graphene is capable of achieving a
capacitance of up to 550 F/g .

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Graphene
• Both major surfaces of graphene sheet are exterior and are readily
accessible by electrolyte
• To utilize the highest intrinsic surface capacitance and specific surface
area of single layer graphene,
• measures were taken to prevent graphene sheets from restacking
themselves during all phases of graphene preparation and
subsequent electrode production procedures,
• these can be ensured by preparing curved graphene sheets and
that will not restack face to face.
• Energy density of 85.6 Wh/kg at room temperature and 136 Wh/kg at
80 °C measured at a current density of 1 A/g were obtained
• Graphene material used in supercapacitor electrodes yielded a high
capacitance of 205 F/g at 1.0 V using an aqueous electrolyte, having
an energy density of 28.5 Wh/kg, the results obtained are significantly
higher than those of carbon based supercapacitors electrode.
Ref: S.R.C Vivekchand, C.S. Rout, K.S. Subrahmanyam, A. Govindaraj and C.N.R. Rao, J. Chem. Sci.,120(2008)9

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To find a more a suitable method for using graphene as supercapacitor
electrode material, three different methods were researched
1. thermal exfoliation of graphitic oxide,
2. graphene was obtained by heating nano-diamond at 1650 oC in a
helium atmosphere, and in,
3. camphor decomposition over nickel nano-particles.
• Highest specific capacitance of 117F/g and an energy density of 31.9
Wh/kg were obtained from thermal exfoliation of graphitic oxide
Graphene from modified hummer’s method and tip sonication method
• Even at a high current of 7.5 A/g the energy and power density
obtained were 58.25 Wh/kg and 13.12 kW/kg respectively, thus
making it possible to be used for electric vehicle applications.
Low temperature exfoliated graphene showed good energy storage
performance, capacitance obtained is higher compared to high
temperature exfoliated graphene
Ref: W. Lv, D.M. Tang, Y.B. He, C.H. You, Z.Q. Shi, X.C. Chen, C.M. Chen, P.X. Hou, C. Liu and Q.H. Yang, Acsnano, 3 (2009) 3730

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Metal oxide
• Metal oxide exhibit high specific capacitance and low resistance,
making it simpler to construct supercapacitors with high energy
and power
The commonly used metal oxides are
• nickel oxide (NiO),
• ruthenium dioxide (RuO2),
• manganese oxide (MnO2),
• iridium oxide (IrO2).
• The lower cost of production and use of a milder electrolyte make
them a feasible alternative

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Ruthenium oxide (RuO2)
• It has unique combination of characteristics like,
catalytic activities, metallic conductivity, electrochemical
reduction-oxidation properties, high chemical and thermal
stability and field emitting behaviour.
• It has the advantages of long cycle life, wide potential window of
high specific capacitance, highly reversible reduction-oxidation
reaction, and metallic type conductivity.
• The resulting electrodes were stable for large number of cycles
yielding a specific capacitance of 498 F/g at a scan rate of 5mV/s
Ref: T. P. Gujar, W.Y. Kim, I. Puspitasari, K.D. Jung and O.S. Joo, Int. J. Electrochem. Sci., 2 (2007) 666

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Nickel oxide
• Environmental friendliness, easy synthesis and low cost.
• Among the benefits of electrochemical strategy include reliability,
simplicity, accuracy, low cost and versatility.
• Ultra high specific capacitance of 1478 F/g in 1 M KOH aqueous
solution electrolyte
Ref: H.Y. Wu and H.W. Wang, Int. J. Electrochem. Sci., 7 (2012) 4405.
asymmetric supercapacitor based on a novel ternary graphene/nickel/nickel
oxide and porous carbon electrode

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Manganese oxide
• Unique physical and chemical properties with a wide range of
applications in ion exchange, catalysis, biosensor, energy storage
and molecular adsorption.
• A special interest is given to manganese dioxide MnO2 as an
electrode material for supercapacitors due to its low cost, excellent
capacitive performance in aqueous electrolytes and environmental
benignity
rechargeable mechanism of manganese dioxide based
symmetric supercapacitors

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Conducting polymers
• Conducting polymers have a relatively high conductivity and
capacitance and equivalent series resistance when compared with
carbon based electrode materials.
• Reduction-oxidation process is used to store and release charge.
• If oxidation occurs also known as doping, ions are been
transferred to the polymer back bone.
• If reduction occurs also known as de-doping, in that case ions
are released back into the solution
• Due to the reduction-oxidation in conducting polymers these
causes a mechanical stress which in turn limits the stability
through many charge-discharge cycles

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Polyaniline (PANI)
• High conductivity, easy synthesis, excellent capacity for energy
storage and low cost [75].
• However, due to repetitive cycles (charge/discharge process)
swelling and shrinkage, PANI is susceptible to rapid degradation in
performance.
• To avoid this limitation, combining PANI with carbon materials has
proved to reinforce the stability of PANI as well as maximize the
capacitance value

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NANO COMPOSITES BASED ELECTRODE MATERIALS
Composite electrodes integrate carbon based material with either
metal oxide or conducting polymer materials, which in turn offers
both physical and chemical charge storage mechanism together in a
single electrode
Carbon-Carbon composites
Carbon-Metal oxides composites
Carbon-Conducting polymer composites
use of two different electrode
materials uses three different electrode
materials to form single
electrode.
composites
Binary Ternary

32. Applications
• Regenerative braking
• Releasing the power in acceleration
• Starting power in start-stop systems
• Regulate voltage to the energy grid
• Capture power when lowering loads and assisting
when loads are lifted
• Back-up power in any application where quick
discharge ( or charge) is required
• Can be used in transport (trams, cars etc…)
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• When compared with other energy storage devices they
give long life, high power, flexible packaging, wide
thermal range (-40oC to 70oC), low maintenance and
low weight .
• Supercapacitors can best be utilized in areas that require
applications with short load cycle and high reliability, for
example energy recapture sources such as forklifts, load
cranes and electric vehicles, power quality improvement
• Among the promising applications of supercapacitors is
in fuel cell vehicles and low emission hybrid vehicles
• Supercapacitors with its unique qualities when used
with batteries or fuel cells they can serve as temporary
energy storage devices providing high power capability
to store energy from braking

34. Conclusion and future scope
• Supercapacitors can be used with or as alternative to
batteries
• It can be very quickly charged/discharged many number
of times (millions)
• It can be used in applications where short bursts of
energy is needed
• Capacitances from 1 Farad to hundreds of Farads or
even thousands can be made
• Voltage range can be maintained from 2-5 volts
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• Supercapacitors can store more than 100X the energy of a
dielectric capacitor (6–8 Wh/kg)
• With carbon materials, a high specific surface area and rational
pore distribution were achieved, even though their capacitances
and energy density are still low.
• Conducting polymers show high specific capacitance, but the
major challenges faced are their swelling and shrinking when
charging and discharging, leading to short lifetime.
• In the case of metal oxides, they also posses high specific surface
area and favor diffusion of ions onto the bulk of material.
• Current supercapacitors in the market can be used for applications
that require a combination of high power delivery for a short time,
high cycling stability, short charging time and long shelf life.
• Work on better methods that will curb the issue of self discharge
in supercapacitors.

36. Thank you
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37. Questions
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